Fair Value Disclosures - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Assets:
Total available-for-sale securities	$ 314,283,000	$ 336,281,000
Fair Value Measured on Recurring Basis [Member]
Assets:
Total available-for-sale securities	314,283,000	336,281,000
Total assets	315,071,000	336,627,000
Liabilities:
Total liabilities	6,894,000	501,000
Fair Value Measured on Recurring Basis [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	4,845,000	4,708,000
Fair Value Measured on Recurring Basis [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	121,844,000	128,148,000
Fair Value Measured on Recurring Basis [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	102,774,000	107,657,000
Fair Value Measured on Recurring Basis [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	13,643,000	35,480,000
Fair Value Measured on Recurring Basis [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	3,725,000	7,201,000
Fair Value Measured on Recurring Basis [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	54,440,000	33,840,000
Fair Value Measured on Recurring Basis [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	11,675,000	16,900,000
Fair Value Measured on Recurring Basis [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	1,337,000	2,347,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	788,000	321,000
Fair Value Measured on Recurring Basis [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	241,000
Fair Value Measured on Recurring Basis [Member] | Forward Loan Sale Commitments [Member]
Assets:
Interest rate locks with customers		25,000
Liabilities:
Derivative liabilities	112,000
Fair Value Measured on Recurring Basis [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	6,541,000	501,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member]
Assets:
Total available-for-sale securities	17,857,000	23,955,000
Total assets	17,857,000	23,955,000
Liabilities:
Total liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	4,845,000	4,708,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	11,675,000	16,900,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	1,337,000	2,347,000
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	0	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Interest rate locks with customers		0
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 1 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member]
Assets:
Total available-for-sale securities	296,426,000	312,326,000
Total assets	297,214,000	312,672,000
Liabilities:
Total liabilities	353,000	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	121,844,000	128,148,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	102,774,000	107,657,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	13,643,000	35,480,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	3,725,000	7,201,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	54,440,000	33,840,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	788,000	321,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	241,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Interest rate locks with customers		25,000
Liabilities:
Derivative liabilities	112,000
Fair Value Measured on Recurring Basis [Member] | Level 2 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member]
Assets:
Total available-for-sale securities	0	0
Total assets	0	0
Liabilities:
Total liabilities	6,541,000	501,000
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | U.S. Treasuries [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | U.S. Government Corporations and Agencies [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | State and Political Subdivisions [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Residential Mortgage-Backed Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Collateralized Mortgage Obligations [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Corporate Bonds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Money Market Mutual Funds [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Equity Securities [Member]
Assets:
Total available-for-sale securities	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Interest Rate Locks with Customers [Member]
Assets:
Interest rate locks with customers	0	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Interest Rate Swap [Member]
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Forward Loan Sale Commitments [Member]
Assets:
Interest rate locks with customers		0
Liabilities:
Derivative liabilities	0
Fair Value Measured on Recurring Basis [Member] | Level 3 [Member] | Contingent Consideration Liability [Member]
Liabilities:
Derivative liabilities	$ 6,541,000	$ 501,000